This invention relates to a communications system for use with meters employed by electrical utilities for automatically monitoring electrical usage; and more particularly, to an improvement which allows for better response from a meter when polled by the master station of a utility.
Automated meter reading or AMR employs specially designed electrical meters installed by a utility at each premises serviced by the utility. Use of AMR allows the utility to separately address each meter to ascertain the amount of electricity usage at the home or building, as well other information (times of peak usage, for example) so to allow the utility to better configure their distribution network to service their customers.
As currently implemented in a TWACS® system employed by the assignee of the present invention, a signal (an outbound signal) is impressed on the electrical lines leading to a facility and as the electricity passes through the meter, the signal is received and processed. The signal may, for example, request that a return signal (an inbound signal) be transmitted back from that location over the same electrical lines with information (data) as to the electrical usage at that location.
When the response signal is generated, it produces high current pulses in a fixed value resistor or other resistive element which is part of a communications module installed in the meter. As is well-known in the art, when current passes through a resistor, electrical energy is converted into heat. This heat then dissipates throughout the meter housing raising the ambient temperature of air within the enclosure and affecting other electrical components installed in the meter. The performance of electronic circuits is adversely affected by the heat, if the heat drives the component's operating temperature above the upper limit of a preferred range of temperatures. Circuit calibrations and the accuracy of information produced by a circuit are affected, and excessive component temperatures will cause the circuits to act erratically, or even fail. All of this, of course, is detrimental to operation of the meter and communications between the master station and meter site.
Recently, an issue was noticed with respect to AMRs communicated with through TWACS. The AMRs now employ a communications module designed for a 17 amp inbound signal current and a 32 byte message burst rate for a nominal 240V. circuit. In attempting to increase inbound signal strength to overcome certain field problems, it was found necessary to increase the inbound signal current from 17 to 21 amps. Since heat generated in a resistor is directly proportional to the square of the current, the increase in current resulted in a more than 50% increase in heat for an inbound signal message having the same 32 byte message length as before. Further testing demonstrated that to maintain the same heating effects as before the signal current was increased, the maximum message length had to be reduced to 18 bytes from 32 bytes. Because of the resulting loss of information which would be transmitted in a single message of this reduced length, this was an unacceptable result.
The present invention is directed at a solution to this and similar problems. As described herein, use of the invention enables the previous 32 byte message length to be retained, even though the current is at the higher level required to increase inbound signal strength. Alternatively, message length of the inbound signal can be increased without increasing the signaling current level. It is also possible to increase both message length and signal current, to a certain extent, while maintaining temperature within a meter within safe limits. The present invention is applicable to all of the above possible scenarios.